Dynamic filter

ABSTRACT

The current invention is intended to render artifacts, which are introduced by changes in coefficients in an FIR filter, inaudible by applying a window to the filtered signal that results in the output of the filter (e.g. FIR filter), in which the coefficients are being changed, supplying little or none of the total output while the output of the filter, in which the coefficients are stable, supplies most or all of the total output.

CROSS-REFERENCE

This application is a continuation of PCT Application No.PCT/US19/26352, filed Apr. 8, 2019; which claims the benefit of U.S.Provisional Application No. 62/655,155, filed Apr. 9, 2018; the entirecontents of which are herein incorporated by reference.

BACKGROUND OF THE INVENTION

In contact hearing systems (e.g., light-driven or inductively-coupled),such as those available from Earlens Corporation, dynamicfrequency-dependent gain in the signal processing system may beimplemented by a finite impulse response (“FIR”) filter withcoefficients that change over time. Changes in coefficients canintroduce brief audible artifacts in the device output. In priordevices, audible artifacts due to filter changes were reduced by slowingand smoothing those changes.

SUMMARY

Aspects of the current invention are intended to render artifacts, whichare introduced by changes in coefficients in an FIR filter, inaudible byapplying a window to the filtered signal that results in the output ofthe filter (e.g., FIR filter), in which the coefficients are beingchanged, supplying little or none of the total output while the outputof the window, in which the coefficients are stable, supplies most orall of the total output.

One method of reducing or eliminating audible artifacts may includeindividually interpolating each filter coefficient by a weightingequivalent to the window values described with respect to the presentinvention. However, since the interpolation would need to be applied toall coefficients at every output sample, use of the windowing methodaccording to the present invention, as described herein, would be a muchmore efficient way of preventing audible artifacts resulting from thechange in coefficients.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of embodimentsof the present inventive concepts will be apparent from the moreparticular description of preferred embodiments, as illustrated in theaccompanying drawings in which like reference characters refer to thesame or like elements. The drawings are not necessarily to scale,emphasis instead being placed upon illustrating the principles of thepreferred embodiments.

FIG. 1 is a cutaway view of an ear canal showing a light-coupled contacthearing system for use in the present invention, wherein at least aportion of the contact hearing system is positioned in the ear canal.

FIG. 2 is a cutaway view of an ear canal showing an inductively coupledcontact hearing system according to the present invention, wherein atleast a portion of the contact hearing system is positioned in the earcanal.

FIG. 3 is a block diagram of a light-coupled contact hearing system foruse in the present invention.

FIG. 4 is a block diagram of an inductively coupled contact hearingsystem for use in the present invention.

FIG. 5 is a top view of an inductively coupled contact hearing devicefor use in systems and methods according to the present invention.

FIG. 6 is a bottom view of an inductively coupled contact hearing devicefor use in systems and methods according to the present invention.

FIG. 7 is a cutaway view of an ear canal illustrating the positioning ofan inductively coupled contact hearing device for use in systems andmethods according to the present invention.

FIG. 8 is a system wherein a data transmission device (e.g., a cellphone) is transmitting a data stream to a contact hearing systemincluding an ear tip and a contact hearing device according to thepresent invention.

FIG. 9 is a block diagram of a dual FIR dynamic filter according to thepresent invention.

FIG. 10 is a graph illustrating the relative values of window A andwindow B in a dual FIR dynamic filter according to the presentinvention.

FIG. 11 is a graph illustrating the timing of the interaction of thewindow A and B values with the filter coefficients in a dual FIR dynamicfilter according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a cutaway view of an ear canal showing a light-coupled contacthearing system for use in the present invention, wherein at least aportion of the contact hearing system is positioned in the ear canal.FIG. 1 is a cutaway view of an ear canal showing a contact hearingsystem 110 for use in the present invention, wherein the contact hearingsystem 110 is positioned in the ear canal. In embodiments of theinvention, contact hearing system 110 may comprise a contact hearingsystem using light to transmit information and/or power from the ear tipto the contact hearing device. In FIG. 1, contact hearing system 110includes audio processor 132, which audio processor may include at leastone external microphone 310. Audio processor 132 may be connected to anear tip 120 by cable 260, which is adapted to transmit signals fromaudio processor 132 to ear tip 120. Taper tube 250 may be used tosupport cable 260 at ear tip 120. Ear tip 120 may further include canalmicrophone 312 and acoustic vent 338. Ear tip 120 may be a light tipwhich radiates light pulses 142 in response to signals from audioprocessor 132. Light or other signals radiated by ear tip 120 may bereceived by contact hearing device 112, which may comprise photodetector130, microactuator 140, and umbo lens 220. Contact hearing device 112may be positioned on tympanic membrane TM.

FIG. 2 is a cutaway view of an ear canal showing a contact hearingsystem 110 for use in systems and methods according to the presentinvention, wherein at least a portion of the contact hearing system 110is positioned in the ear canal. In embodiments of the invention, contacthearing system 110 may comprise a contact hearing system usingelectromagnetic waves 145 to transmit information and/or power from eartip 120 to the contact hearing device 112. In embodiments of theinvention, contact hearing system 110 may comprise a contact hearingsystem using inductive coupling to transmit information and/or powerfrom ear tip 120 to contact hearing device 112. In FIG. 2, contacthearing system 110 may include audio processor 132, which audioprocessor may include at least one external microphone 310. Audioprocessor 132 may be connected to an ear tip 120 by cable 260, which isadapted to transmit signals from audio processor 132 to ear tip 120. Eartip 120 may further include canal microphone 312 and at least oneacoustic vent 338. Ear tip 120 may be an ear tip which radiateselectromagnetic waves 145 in response to signals from audio processor132. Electromagnetic signals radiated by ear tip 120 may be received bycontact hearing device 112, which may comprise receive coil 131,microactuator 140, and umbo lens 220. Contact hearing device 112 mayfurther include grasping tab 114.

FIG. 3 is a block diagram of a light-coupled contact hearing system foruse in the present invention, wherein the contact hearing system 110 maybe positioned in the ear canal of a user. In embodiments of theinvention, contact hearing system 110 may include one or more externalcommunication and control devices 324, which may also act as a datatransmission device 400 (as in FIG. 6). In embodiments of the invention,audio processor 132 may communicate with external communication andcontrol devices 324 by, for example, using audio processor antenna 134.In FIG. 3, contact hearing system 110 may include audio processor 132,ear tip 120, and contact hearing device 112. Audio processor 132 mayinclude external microphone 310, audio processor antenna 134, analog todigital converter 320, and signal processor 330. Audio processor 132 maybe connected to ear tip 120 by cable 260. Ear tip 120, which may also bereferred to as a light tip, may include a light source 290 (which may bea laser), acoustic vent 338, and canal microphone 312. Signals,including data and power, may be transmitted from ear tip 120 to contacthearing device 112 using light, such as light pulses 142. Contacthearing device 112 may include photodetector 130, microactuator 140, andumbo lens 220. Umbo lens 220 may be positioned to contact tympanicmembrane TM. In FIG. 3, acoustic input 340 (which may be an ambientsound or an audible sound) may be received by external microphone 310 ofaudio processor 132, which then processes the received sound by passingit through processing circuitry, which may include analog to digitalconverter 320 and signal processor 330.

FIG. 4 is a block diagram of a contact hearing system 110 for use in thepresent invention. In embodiments of the invention, at least a portionof contact hearing system 110 is positioned in the ear canal of a user.In FIG. 4, acoustic input 340 may be received by external microphone 310of audio processor 132, which then processes the received sound bypassing it through processing circuitry, which may include analog todigital converter 320 and signal processor 330. The output of audioprocessor 132 may be transmitted to an ear tip 120 by cable 260. Signalstransmitted to ear tip 120 may then be transmitted to contact hearingdevice 112 by, for example, causing transmit coil 292 to radiateelectromagnetic waves 145. In embodiments of the invention, contacthearing device 112 may include receive coil 131, demodulator 116,microactuator 140, and umbo lens 220. Information contained inelectromagnetic waves 145 received by receive coil 131 may betransmitted through demodulator 116 to microactuator 140, moving umbolens 220. In embodiments of the invention, the signal transmitted to eartip 120 may be a signal representative of the received audio signal,which may then be transmitted to contact hearing device 112. Inembodiments of the invention, transmit coil 292 may be wound around anacoustic vent 338 in ear tip 120. In embodiments of the invention,acoustic vent 338 may be formed as a passage through a ferrite material.In embodiments of the invention, transmit coil 292 may be wound aroundferrite material positioned in ear tip 120. In embodiments of theinvention, contact hearing system 110 may include one or more externalcommunication and control devices 324, such as, for example, a cellphone. In embodiments of the invention, audio processor 132 maycommunicate with external communication and control devices 324 by, forexample, using audio processor antenna 134. Umbo lens 220 may bepositioned to contact tympanic membrane TM. Ear tip 120 may includecanal microphone 312.

FIG. 5 is a top view of a contact hearing device 112 according to thepresent invention. FIG. 6 is a bottom view of a contact hearing device112 according to the present invention. The contact hearing device 112illustrated in FIGS. 5 and 6 includes a receive coil 131, amicroactuator 140, an umbo lens 220, a support structure 141, andsprings 144. In the embodiment illustrated in FIGS. 5 and 6,microactuator 140 is connected to support structure 141 by springs 144.In embodiments of the invention, contact hearing device 112 may furtherinclude a sulcus platform 118, which may also be referred to as amounting platform, connected to support structure 141 and adapted toassist in positioning contact hearing device 112 in the ear canal of auser. In embodiments of the invention, contact hearing device 112 mayfurther include grasping tab 114.

FIG. 7 is a cutaway view of an ear canal illustrating the positioning ofa contact hearing device 112 according to the present invention. In theembodiment of FIG. 7, contact hearing device 112 is positioned at amedial end of the ear canal, proximate the tympanic membrane of theuser. Contact hearing device 112 includes a receive coil 131 positionedat a proximal end thereof. In embodiments of the invention, receive coil131 may be positioned to receive signals from an ear tip (not shown)positioned in the ear canal lateral to the position of contact hearingdevice 112. In embodiments of the invention, signals received by receivecoil 131 may be transmitted to microactuator 140 to move drive post 124which is connected to the user's tympanic membrane through umbo lens220. Umbo lens 220 may be in direct physical contact with the tympanicmembrane or a thin layer of oil 126 may be used between umbo lens 220and the user's tympanic membrane. Sulcus platform 118 may be used toproperly position contact hearing device 112 in the user's ear canalthrough contact with a skin layer which lines the ear canal. Sulcusplatform 118 may be in direct contact with the skin of the ear canal, ora thin layer of oil 126 may be used between sulcus platform 118 and theskin of the ear canal. In embodiments of the invention, contact hearingdevice 112 may further include support structure 141, grasping tab 114and springs 144.

FIG. 8 is a system wherein a data transmission device such as a cellphone is transmitting a data stream to a contact hearing systemincluding an ear tip and a contact hearing device according to thepresent invention. In FIG. 8, data transmission device 400 includes adata transmission antenna 402 from which data, such as streaming audio,may be transmitted to a receiver antenna 404, which is connected toreceiver 406. The output of receiver 406 may be transmitted to signalprocessor 330. Signal processor 330 may include a sampling rateconverter and a digital signal processor. The output of signal processor330 may be transmitted to ear tip 120, which may transmit the output ofsignal processor 330 via transmitted signal 412. Transmitted signal 412may comprise light pulses or other electromagnetic waves, includingradio waves and inductively coupled waves. Transmitted signal 412 may bereceived by contact hearing device 112 and converted to mechanicalenergy to drive a tympanic membrane through, for example, umbo lens 220.

In FIG. 9 an input signal 1100 is received by filter A 1102 and filter B1104. Coefficient values 1106 are fed into filter A by coefficientupdate and window logic 1108. Coefficient values 1110 are fed intofilter B by coefficient update and window logic 1108. Output 1112 offilter A is transmitted to one input of multiplier 1116. Output 1114 offilter B is transmitted to one input of multiplier 1118. A second inputof multiplier 1116 receives a window A value 1120 which is generated bycoefficient and update logic 1108. A second input of multiplier 1118receives a window B value which is generated by coefficient update andwindow logic 1108. Output 1126 of multiplier 1116 is summed with output1128 of multiplier 1118 in summing circuit 1124 to generate filtersystem output 1130.

FIG. 10 is a graph illustrating the relative values of window A andwindow B in a dual FIR dynamic filter according to the presentinvention.

FIG. 11 is a graph illustrating the timing of the interaction of thewindow A and B values with the filter coefficients. In the embodiment ofFIG. 11, filter coefficients X0 are loaded into filter A at time T1.Note that, in the graph illustrated in FIG. 11, filter B would havereceived its most recent update prior to time T1. At time T1, the valueof window A is zero, thus the output of filter A will have no impact onthe overall filter system output. Between time T1 and time T2, a new setof filter coefficients X1 are calculated while the relative contributionof the output of filter A to the overall filter system output increasesin accordance with the value of window A, while the relativecontribution of the output of filter B declines with the value of windowB. At time T2, the contribution of filter B has declined to zero and thefilter system output is made up of the output of filter A. At time T2,the newly calculated coefficients X1 are loaded into filter B. Becausethe filter system output is comprised of only the output of filter A,when the new coefficients are loaded, any anomalies or audible artifactscaused by updating the coefficients in filter B will not be present inthe filter system output.

A dual FIR filter system according to the present invention is depictedin FIG. 9. In embodiments of the invention, two FIR filters operate inparallel; that is, they are applied simultaneously to the same inputsignal after which a tapered window is applied to the output of eachfilter. In the embodiment of FIG. 9, the windows are complementary, inthe sense that their sum is always equal to one. In one embodiment ofthe invention, when Window A has a value of 1.0 (no attenuation of theoutput of filter FIR A), Window B then has the value 0.0 (fullattenuation of filter FIR B). As the value of Window A tapers to 0, thevalue of Window B simultaneously rises to 1. As illustrated in FIG. 10,the two windows alternate in this manner, with one window alwaysapproaching 1, and the other always approaching 0, so that when onefilter's output is completely un-attenuated, the other is fullyattenuated. It will be apparent that other waveforms, such as, forexample complementary step function waveforms may be uses to achieve thegoal of having Window B have a value of 1 when Window B has a value ofzero.

As illustrated in FIG. 11, between time T2 and time T3 a new set offilter coefficients X2 are calculated while the relative contribution ofthe output of filter B to the overall filter system output increases inaccordance with the value of window B, while the relative contributionof the output of filter A declines with the value of window A. At timeT3, the contribution of filter A has declined to zero and the filtersystem output is made up of the output of filter B. At time T3, thenewly calculated coefficients X2 are loaded into filter A. Because thefilter system output is comprised of only the output of filter B, whenthe new coefficients are loaded, any anomalies or audible artifactscaused by updating the coefficients in filter A will not be present inthe filter system output.

As illustrated in FIG. 11, between time T3 and time T4 a new set offilter coefficients X3 are calculated while the relative contribution ofthe output of filter A to the overall filter system output increases inaccordance with the value of window A, while the relative contributionof the output of filter B declines with the value of window B. At timeT4, the contribution of filter B has declined to zero and the filtersystem output is made up of the output of filter A. At time T4, thenewly calculated coefficients X1 are loaded into filter B. Because thefilter system output is comprised of only the output of filter A, whenthe new coefficients are loaded, any anomalies or audible artifactscaused by updating the coefficients in filter B will not be present inthe filter system output.

The present invention renders artifacts caused by changes in the FIRfilter coefficients inaudible by applying the coefficient changes onlyduring the time when the corresponding filter is fully attenuated by itswindow. That is, a filter is changed only when its output is inaudible.When the window rises and that filter is no longer attenuated, anytransient artifacts due to the coefficient changes are likely to havepassed, and the coefficients in the other (now attenuated) filter cansafely be changed. In this way, coefficients in one filter are changedonly while its output is inaudible.

In embodiments of the invention, there is added latency in theapplication of gain changes, so this invention is most appropriate in anapplication in which some gain changes can be smooth and slow relativeto the coefficient update rate. As an example, embodiments of thepresent invention may include the use of dual dynamic FIR filters inhearing aids which utilize Wide Dynamic Range Compression (WDRC).

In embodiments of the invention, the output of two windowed filters aresummed to compose the overall system output. The complementary nature ofthe two windows ensures that the amplitude modulation of the individualfilter output signals is not audible. Coefficient changes thatdynamically apply frequency-dependent gain are applied to the filtersalternately, and only when the corresponding filter output (and anyconsequent artifacts) are fully attenuated and therefore inaudible. Insystems according to the present invention, filter coefficient changesare calculated on a block basis (every N samples, where N>1), and thewindow period is equal to twice the block length (2*N), so that filtersare updated (coefficients changed) in alternate blocks.

Embodiments of the present invention may be applied to any dynamicfilter system requiring real time coefficient changes, includingrecursive filters, such as, for example infinite impulse response (IIR)filters. In such recursive filters, artifacts due to coefficient changeswill be attenuated as long as the impulse response of the filter isconcentrated near zero delay. A recursive filter with a sharp resonance,for example, may not benefit as much from the current invention as aminimum phase FIR filter. In embodiments of the invention, includingthose used with recursive filters, more than 2 windows and filters maybe employed to increase the time elapsed between coefficient updates andaudibility of the output of the corresponding filter. In embodiments ofthe invention, the use of more than two windows and filters may resultin additional expense, complexity, and gain latency.

In embodiments of the invention, the invention may be used as acomponent of, or method in, a contact hearing system.

Embodiments of the present invention are directed to a signal filtersystem for use in a contact hearing system, the signal filter systemincluding: a signal input connected to a first filter and a secondfilter; a first coefficient input connected to the first filter; asecond coefficient input connected to the second filter; coefficientupdate and window logic connected to the first and second coefficientinputs; a first window generator connected to the coefficient update andwindow logic; a second window generator connected to the coefficientupdate and window logic; a first multiplier receiving inputs from thefirst filter and the first window generator; a second multiplierreceiving inputs from the second filter and the second window generator;and a summing circuit receiving inputs from the first and secondmultiplier circuits. Embodiments of the invention may further include asignal filter wherein the first and second filters are FIR filters.

Embodiments of the present invention are directed to a method forfiltering a signal in a contact hearing system, wherein the methodcomprises the steps of: providing the signal simultaneously to a firstfilter and a second filter; providing the first filter with a firstcoefficient for use in filtering the input signal, wherein the firstcoefficient is provided to the first filter at a first time; providingthe second filter with a second coefficient for use in filtering theinput signal at a second time, wherein the second time is after thefirst time; multiplying an output of the first filter by a first windowvalue to get a first filter value; multiplying an output of the secondfilter by a second window value to get a second filter value; and addingthe first filter value to the second filter value. Embodiments of thepresent invention are further directed to a method wherein the firsttime occurs when the first window value is at or near a minimum value.Embodiments of the present invention are further directed to a methodwherein the first time occurs when the first window value issubstantially equal to zero. Embodiments of the present invention arefurther directed to a method wherein the second time occurs when thesecond window value is at or near a minimum value. Embodiments of thepresent invention are further directed to a method wherein the secondtime occurs when the second window value is substantially equal to zero.Embodiments of the present invention are further directed to a methodwherein the first time occurs when the first window value is less thanthe second window value. Embodiments of the present invention arefurther directed to a method wherein the second time occurs when thesecond window value is less than the first window value.

Embodiments of the present invention are directed to a method forfiltering a signal in a contact hearing system, wherein the methodcomprises the steps of: providing the signal simultaneously to a firstfilter and a second filter; changing at least one coefficient in thefirst filter to a first coefficient, wherein the first coefficient ischanged in the first filter at a first time; changing at least onecoefficient in the second filter to a second coefficient, wherein thesecond coefficient it changed in the second filter at a second time, andwherein the second time is after the first time; multiplying an outputof the first filter by a first window value to get a first filter value;multiplying an output of the second filter by a second window value toget a second filter value; and adding the first filter value to thesecond filter value.

Definitions

Audio Processor—A system for receiving and processing audio signals.Audio processors may include one or more microphones adapted to receiveaudio which reaches the user's ear. The audio processor may include oneor more components for processing the received sound. The audioprocessor may include digital signal processing electronics and softwarewhich are adapted to process the received sound. Processing of thereceived sound may include amplification of the received sound. Theoutput of the audio processor may be a signal suitable for driving alaser located in an ear tip. The output of the audio processor may be asignal suitable for driving an antenna located in an ear tip. The outputof the audio processor may be a signal suitable for driving an inductivecoil located in an ear tip. Audio processors may also be referred to asbehind the ear units or BTEs.

Contact Hearing System—A system including a contact hearing device, anear tip and an audio processor. Contact hearing systems may also includean external communication device. An example of such system is anEarlens hearing-aid that transmits audio signal by laser to a contacthearing device which is located on or adjacent to the ear drum. Thecontact hearing system may also be referred to as a smart lens.

Contact Hearing Device—A tiny actuator connected to a customizedring-shaped support platform that floats on the ear canal around theeardrum, where the actuator directly vibrates the eardrum causing energyto be transmitted through the middle and inner ears to stimulate thebrain and produce the perception of sound. The contact hearing devicemay comprise a photodetector, a microactuator connected to thephotodetector, and a support structure supporting the photodetector andmicroactuator. The contact hearing device may comprise an antenna, amicroactuator connected to the antenna, and a support structuresupporting the antenna and microactuator. The contact hearing device maycomprise a coil, a microactuator connected to the coil, and a supportstructure supporting the coil and microactuator. The contact hearingdevice may also be referred to as a Tympanic Contact Actuator (TCA), aTympanic Lens, a Tympanic Membrane Transducer (TMT), or a smart lens.

Ear Tip—A structure designed to be placed into and reside in the earcanal of a user, where the structure is adapted to receive signals froman audio processor and transmit signals to the user's tympanic membraneor to a device positioned on or near the user's tympanic membrane (suchas, for example, a contact hearing device). In one embodiment of theinvention, the signals may be transmitted by light, using, for example,a laser positioned in the light tip. In one embodiment of the invention,the signals may be transmitted using radio frequency, using, forexample, an antenna connected to the Ear Tip. In one embodiment of theinvention, the signal may be transmitted using inductive coupling,using, for example, a coil connected to the ear tip. The ear tip mayalso be referred to as a light tip, magnetic tip, or mag tip.

Light-Driven Hearing Aid System—A contact hearing system wherein signalsare transmitted from an ear tip to a contact hearing device using light.In a light driven hearing system, light (e.g. laser light) may be usedto transmit information, power, or both information and power to acontact hearing device.

RF-Driven Hearing Aid System—A contact hearing system wherein signalsare transmitted from an ear tip to a contact hearing device using radiofrequency electromagnetic radiation. In an RF driven hearing system,electromagnetic radiation may be used to transmit information, power, orboth information and power from the ear tip to the contact hearingdevice.

Inductively-Driven Hearing Aid System—A contact hearing system whereinsignals are transmitted from an ear tip to a contact hearing deviceusing inductive coupling. In an inductively driven hearing system,magnetic waves may be used to transmit information, power, or bothinformation and power from the ear tip to the contact hearing device.

Light Tip—An ear tip adapted for use in a light driven hearing aidsystem. A light tip may include a laser.

Mag Tip—An ear tip adapted for use in an inductively driven hearing aidsystem. The mag tip may include an inductive transmit coil.

While the preferred embodiments of the devices and methods have beendescribed in reference to the environment in which they were developed,they are merely illustrative of the principles of the present inventiveconcepts. Modification or combinations of the above-describedassemblies, other embodiments, configurations, and methods for carryingout the invention, and variations of aspects of the invention that areobvious to those of skill in the art are intended to be within the scopeof the claims. In addition, where this application has listed the stepsof a method or procedure in a specific order, it may be possible, oreven expedient in certain circumstances, to change the order in whichsome steps are performed, and it is intended that the particular stepsof the method or procedure claim set forth herebelow not be construed asbeing order-specific unless such order specificity is expressly statedin the claim.

REFERENCE NUMBERS Number Element 110 Contact Hearing System 112 ContactHearing Device 114 Grasping Tab 116 Demodulator 118 Sulcus Platform 120Ear Tip/Light Tip/Mag Tip 124 Drive Post 126 Oil Layer 130 Photodetector131 Receive Coil 132 Audio Processor 134 Audio Processor Antenna 140Microactuator 141 Support Structure 142 Light Pulses 145 ElectromagneticWaves 144 Springs 220 Umbo Lens 250 Taper Tube 260 Cable 290 LightSource 292 Transmit Coil 310 External Microphone 312 Canal Microphone320 Analog to Digital Converter 324 External Communication and ControlDevice 330 Signal Processor 338 Acoustic Vent 340 Acoustic Input(Audible Sound) 400 Data Transmission Device 402 Data TransmissionAntenna 404 Receiver Antenna 406 Receiver 412 Transmitted Signal TMTympanic Membrane 1100 Input Signal 1102 Filter A 1104 Filter B 1106Coefficient Values for Filter A 1108 Coefficient Update and WindowsLogic 1110 Coefficient Values for Filter B 1112 Output of Filter A 1114Output of Filter B 1116 Multiplier 1118 Multiplier 1120 Window A Value1122 Window B Value 1124 Summing Circuit 1126 Output of Multiplier 111161128 Output of Multiplier 11118 1130 Filter System Output

1. A signal filter system for use in a contact hearing system, thesignal filter system comprising: a signal input connected to a firstfilter and a second filter; a first coefficient input connected to thefirst filter; a second coefficient input connected to the second filter;a coefficient update and window logic connected to the first and secondcoefficient inputs; a first window generator connected to thecoefficient update and window logic; a second window generator connectedto the coefficient update and window logic; a first multiplier receivinginputs from the first filter and the first window generator; a secondmultiplier receiving inputs from the second filter and the second windowgenerator; and a summing circuit receiving inputs from the first andsecond multiplier circuits.
 2. A signal filter system according to claim1, wherein the first and second filters are FIR filters.
 3. A method forfiltering a signal in a contact hearing system, wherein the methodcomprises the steps of: providing the signal simultaneously to a firstfilter and a second filter; providing the first filter with a firstcoefficient for use in filtering the input signal, wherein the firstcoefficient is provided to the first filter at a first time; providingthe second filter with a second coefficient for use in filtering theinput signal at a second time, wherein the second time is after thefirst time; multiplying an output of the first filter by a first windowvalue to get a first filter value; multiplying an output of the secondfilter by a second window value to get a second filter value; and addingthe first filter value to the second filter value.
 4. A method accordingto claim 3, wherein the first time occurs when the first window value isat or near a minimum value.
 5. A method according to claim 4, whereinthe first time occurs when the first window value is substantially equalto zero.
 6. A method according to claim 3, wherein the second timeoccurs when the second window value is at or near a minimum value.
 7. Amethod according to claim 6, wherein the second time occurs when thesecond window value is substantially equal to zero.
 8. A methodaccording to claim 3, wherein the first time occurs when the firstwindow value is less than the second window value.
 9. A method accordingto claim 8, wherein the second time occurs when the second window valueis less than the first window value.
 10. A method for filtering a signalin a contact hearing system, wherein the method comprises the steps of:providing the signal simultaneously to a first filter and a secondfilter; changing at least one coefficient in the first filter to a firstcoefficient, wherein the first coefficient is changed in the firstfilter at a first time; changing at least one coefficient in the secondfilter to a second coefficient, wherein the second coefficient itchanged in the second filter at a second time, and wherein the secondtime is after the first time; multiplying an output of the first filterby a first window value to get a first filter value; multiplying anoutput of the second filter by a second window value to get a secondfilter value; and adding the first filter value to the second filtervalue.